This invention relates to a distributor for an internal combustion engine and, more particularly, to a rotary magnetic shield vane for use in generating a rotation electrical signal in a distributor for an internal combustion engine.
FIGS. 4 and 5 illustrate one example of a conventional distributor for use in an internal combustion engine, in which reference numeral 1 designates housing, 2 designates a cap for covering an open end of the housing 1, and 3 designates a rotary shaft rotatably supported by the housing 1 and connected to an engine crank shaft (not shown) or synchronous rotation therewith.
Reference numeral 4 designates an electric signal generator mounted within the housing 1 and comprising a Hall-effect sensor unit in which a Hall-effect IC magnetic field sensor and a magnet are secured in the housing 1 by a thermo-setting plastic material with a gap 8 provided therebetween. 5 designates a a rotary magnetic shield or a vane made of a magnetic material and attached to the rotary shaft 3 through a blank 6 and a screw 7 for rotation therewith. As best seen in FIGS. 6 and 7, the rotary magnetic shield 3 is a generally disc-shaped member having our bent shield tabs 5a on a peripheral edge of a disc 5d at equal intervals. The shield tabs 5a of the rotary magnetic shield 5 are arranged to pass through the gap 8 formed between the field sensor and the magnet of the electrical signal generator 4 as the rotary magnetic shield is rotated by the rotary shaft 3.
Reference numeral 9 designates a distributor rotor mounted on the rotary shaft 3 for rotation therewith and having an electrode 11 in electrical contact with a center electrode 10 disposed on the cap 2. 12 designates peripheral electrodes disposed around the rotor 9 in correspondence with ignition plugs (not shown) in each engine cylinder (not shown) for receiving distributed secondary voltages from the rotor electrode 11 to generate ignition sparks on the spark plugs.
In the conventional internal combustion engine distributor of the above arrangement, as the rotary magnetic shield 5 mounted to the rotary shaft 3 is rotated by the rotation of the engine crank shaft the tabs 5a of the rotary magnetic shield 5 pass through the magnetic gap 8 in the signal generator 4, and the magnetic flux flowing through the gap 8 from the magnet to the Hall-effect IC sensor is interrupted. This change of magnetic flux in the gap 8 is detected by the Hall-effect IC sensor and an electrical signal indicative of the rotation of the rotary shaft 3 is generated. This signal is supplied to an ignition timing control unit (not shown) where it is used to control the ignition timing of the respective spark plugs in the engine cylinders.
In the conventional rotary magnetic shield 5, the magnetic shield tabs 5a are bent at substantially right angles relative to disc-shaped main body 5d at a small radius of curvature as illustrated by a sharp corners 5c in FIG. 7. Also, the sides of the shield tabs 5a and the periphery of the disc 5d define substantially right-angle corners 5b of a very small radius of curvature. Therefore, during the operation of the internal combustion engine, since the shield vanes or tabs 5a are subjected to engine vibration and centrifugal forces due to a high speed rotation, cracks may generate at the sharp corners 5c and edge corners 5b.